The invention relates to wind energy converters (WECs).
Wind energy has emerged as the fastest growing source of energy, presenting a clean, renewable, and ecological-friendly alternative to traditional fossil-based energy supplies. At the current growth rate, wind energy conversion is projected to produce more than 117,000 MW by the year of 2009, claiming about 1.25% of the world's electricity generation. Currently, wind power is most often utilized in large-scale wind farms for providing electricity to power grids, though sometimes also in individual wind turbines to service rural residences at grid-isolated locations. As the total base of wind capacity continues to grow with the installation of additional wind turbines and new wind farms, compliance with power grid interconnection standards becomes increasingly important.
One interconnection standard, in particular, requires electrical generators (e.g., hydroelectric, thermoelectric, and nuclear generators) to continue to operate during disturbances and remain connected to the grid during voltage drops, a process called “low-voltage ride through” (LVRT). For instance, when the voltage at the terminal of the generator falls under a prescribed level (e.g., due to a short circuit in the grid), power stations with LVRT capability continue to provide electricity to the power grid rather than being switched offline, thereby effectively stabilizing the grid.
However, in certain situations, prior art WECs have been allowed to trip offline during a low voltage event, primarily because wind power contributions were considered insignificant to the entire power capacity in the grid. Once disconnected from the power grid, WECs usually go through a restart cycle without providing power to the grid for several minutes.
Recently, in consideration of the growing trend of wind plant/farm integration to the power grid and its potential influence on grid stability, the Federal Energy Regulatory Commission (FERC) has proposed a LVRT standard on WECs, which requires large wind plants or farms (with a capacity of 20 MW or greater) to stay online and to operate continuously during low-voltage occurrences.